Method of distilling fluids at low temperatures



Dec. 1, 1936. J. w. PACKlE ET AL 2,062,375

METHOD OF DISTILLING FLUIDS AT LOW TEMPERATL IF KES 2 Sheets-Sheet 1 Filed March 6, 1953 Dec. 1, 1936.

J. W. PACKIE ET AL METHOD OF DISTILLINQ FLUIDS AT LOW TEMPERATURES Filed March 6, 1933 2 Sheets-Sheet 2 Patented Dec. 1, 1936 METHOD oF DISTILLING FLUIDS-:ATV Low TEMPERATURES John W. Packie, Green Village, and Daniel Stines, Plainfield, N. J., assignors to: Standard Oil Development Company, a corporation of Delaware Application March 6, 1933, Serial No. 659,594

1 Claim.

This invention relates to an improved method of distilling low boiling point fluids in tubular heaters and has special reference to the vaporization of low boiling fluids at comparatively low temperatures.

This invention relates particularly to a method of vaporizing a mixture of fluids having different low boiling points, which require considerable vaporization such as treated cracked distillate at low pressures and temperatures, in such a manner that the liquid and vapor are maintained in intimate contact and in substantial equilibrium and the distribution of liquid and vapor is maintained uniformly throughout the heating element by the lifting action of the vapors evolved.

An object of this invention is to vaporize the fluids at a comparatively low temperature by heating the fluids at a pressure not substantially greater than the pressure in the fractionating apparatus. It is a further object of this invention to obtain even distribution of the medium being vaporized in the vaporizing elements. It is a further object of this invention to keep the vapors evolved in intimate contact with the fluids and in substantially flash equilibrium.

It is common practice in the distillation of hydrocarbon fluids to arrange several of the horizontal heating elements in a fixed setting in parallel so as to minimize the pressure drop 'in the heating elements and thus secure greater vaporization at the same temperature. However, with this practice it is impracticable to use too large a tube or to arrange too many tubes in parallel as the distribution of the liquids and vapors becomes imperfect and thus local overheating occurs. In this invention, the tubes are vertical and since the pressure at the bottom of each tube is the same, even distribution is obtained. In addition, the arrangement of the tubes covered in this invention is well adapted for the introduction of steam and for the use of a large number of small tubes.

The invention will be best understood if the following description is read in connection with the accompanying drawings, in which Fig. 1 is a diagrammatic elevation of one suitable form of apparatus,

Fig. 2 is a sectional perspective view of the heating element,

Fig. 3 is a side elevation view of the heating element, and

Fig. 4 is a front elevation view of the heating element. 7

Referring to the drawings, numeral I denotes a charging line provided with pump 2 for passing oil to the radiant tubes 3 arranged in a furnace setting 4. Burner 5 is provided for supplying heat to the furnace. Radiant tubes 3 dis charge through line Bto a header l in the bottom of the bundle of heating tubes 8 arranged in heating element 9 and leading to header ll]. Header ID on the top of heating tubes. 8 discharges through an insulated transfer pipe ll disposed on the outside of heating element 9 into the header l2 on th e bottom of the bundleof tubes l3 leading to header l4. Header l4 discharges through line l5 toa separating tower IS. The separating tower It has suitable bubble plates ll, draw-off line l8 provided with pump I9 and cooler 20 whichmay be used as a means topreheat oil. Vapor line'ZI is provided with oil condenser 22, water condenser 23 andq receiving tank 24. Line 25 provided with pump 26 is used to pass the condensate to storage {not shown). Line 21, provided with pump 28 is usedto pass a fraction of the condensate as reflux to the upper portion of separating tower l6.

Referring to Figs.22 to 4, a preferred-typeof a heating element 9 is shown. Openings 29 are provided for the entrance of flue gas from the, furnace to the lower parts of the heating element9.

Two bundles of parallel tubes 8 and I2 verticallymounted are provided with headers 1,111,112 and I 4. and'are disposedin the heating element .9. Transverse line which is suitably insulated connects headers Ill and 2 and passes the oil' from header l0 toheader. l2 and is disposedon' the outsideof heating element 9.. .Twobafilesw30 through which the tubes 8 and I3 pass are extended inwardly from the walls of the heating element 9 leaving a central opening through which the flue gas is allowed to pass upwardly. The baffles 30 are placed in spaced relation to bottom of the heating element 9 and divide the space between bottom .and top of the heating element 9 into two parts. Flue gas outlets 3| opening into stack 32 are provided in the upper part of the heating element 9. Lines 33 and 34 are provided for passing steam into headers l and I2 respectively.

The following example of an operation of the temperature of the oil is raised to the point where the vaporization begins. Other means of preheating the oil may be used and the radiant tubes may be omitted or used for some other pur pose. The preheated oil, at a temperature of 300 F. in this example, is passed through pipe 6 to header 1 and bundle of parallel tubes 8. Steam may or may not be introduced at header 1 though steam is used in this example. The preheated oil in parallel tubes 8 is heated and about 10% is vaporized by the flue gases passing from the radiant heat section of the furnace or from any other source through flue inlets 29 into the heating element 9. The flue gases follow a tortuous path flowing upwardly around the tubes until diverted by the baflles 30 to the central part of the heating element 9. The flue gases upon passing the baflles 30 flow upwardly and around the upper portion of the parallel tubes .and pass out of the heating element 9 through openings 3| to the stack 32. A gage pressure such as 8.55 pounds per square inch is maintained on the oil in tubes 8. g

The oil and vapors pass to header ID on top of tubes 8 and thence through transfer pipe II to header l2 at a temperature of about 290 F. The oil and vapors pass upwardly from header l2 through tubes I3 to header l4 and through outlet l 5 to separator l6. Steam may or may not be introduced in header l2. About 41% of the oil is vaporized in tubes IS. The vapors evolved in the heating tubes are maintained in intimate contact with the unvaporized oil and exert a lifting action and are not separated while passing through the heating element. Low pressures of less than an absolute pressure of pounds per square inch are obtained on the oil passing through the heating element 9 by means of the large number of tubes in parallel and the corresponding low pressure drop.

By furnishing the heat to the charge in the parallel vertical tubes where the vapors are not unduly confined, the large pressure drops that characteristically accompany considerable vaporization in the conventional pipe still heating coils are avoided. By the above means, low temperature vaporization is secured at a low pressure and the formation of undesirable decomposition products is minimized.

The oil is passed to separator l6 at a temperature of about 259 F., where 86.6% of the oil is vaporized and a gage pressure of 2 pounds per squareinch is maintained. The condensate and unvaporized oil are withdrawn through pipe 1 8.

Vapors passing through vapor line 2] are condensed and a fraction may be returned as reflux by pipe 2'! to the top plate of the separator.

In this invention uniform distribution of liquid and vapor in the heating element is secured. vaporization at low temperatures and pressures is maintained which is not normally obtainable without the use of excessive quantities of steam or unreasonablylow fractionating pressures. The invention is especially adapted to rerun cracked distillate to produce motor fuel without excessive use of steam. The desirable temperature limits are not exceeded and undesirable polymerization is avoided.

In this process it is preferred to use a sumcient number of tubes in parallel so that the pressure drop will be such as to allow the progressive vaporization of the liquid due to the heat input obtained with no appreciable change in the sensible heat of the mixture. It is also preferred to use suflicient steam, introduced in the several heating sections, to maintain the desired temperature of vaporization.

The foregoing description is merely illustrative and various changes and alternative arrangements may be made within the scope of the appended claim in which it is our intention to claim all novelty inherent in the invention as broadly as the prior art permits.

We claim:

Method of distilling low boiling liquid hydrocarbons of the type of cracked distillate, without substantial cracking and polymerization due to high pressure drop, comprising forcing the liquid in a single stream of restricted cross section, raising the temperature of said stream to a point just short of substantial vaporization, dividing said stream into a plurality of parallel streams, continuing application of heat to said parallel streams to effect vaporization in the order of 10% of the preheated oil, then combining said streams into a single stream of enlarged cross section, dividing the stream into another plurality of parallel streams, continuing application of heat to said streams to effect vaporization to a total of about 41% of the original oil, again combining said streams into one stream of enlarged cross section, supplying additional heat to said stream under refluxing conditions in a separation zone to effect a total vaporization of about 86.6% of the original oil, and separating the liquid from the vapors in said zone.

JOHN W. PACKIE. DANIEL E. STINES. 

